07-08-25 Agenda Packet - Laserfiche WebLink

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Page 1 of 3 Memorandum (DRAFT) Date: May 7, 2025 To : Honorable Mayor and City Councilmembers Jessica Jagoe, Interim City Administrator From: The Karth Lake Improvement District Board, in coordination with the Rice Creek Watershed District Subject: Karth Lake Level Modeling Project as Pertains to the 2026 PMP Street and Utility Improvement Project The Project: The KLID board initiated a Karth Lake Level Modeling Project in October 2021.1 Purpose: Explore modification to the current lake level pumping plan with the goal of reducing Karth Lake’s extreme high and low lake levels (“bounce”) of 3-5 feet. A reduction in bounce is expected to reduce erosion, improve water quality and improve the health of fish, vegetation and wildlife in and around the lake, as well as discourage expansion of invasive plant species. History: Beginning in the 1970s, land use surrounding Karth Lake began transitioning from agricultural to residential and business use. Surface water management, including installation of street sewers with outlets into Karth Lake, caused a near quadrupling of the watershed: from 41 to 143 acres. These include about 25 acres of impervious surfaces, more than the lake’s normal surface area of 20 acres.2 Karth Lake has no natural outlet and is assigned to the RCWD even though it does not naturally drain into Rice Creek. Since development around the lake began, periods of Karth Lake flooding have occurred and been managed by the City using contractors to temporarily pump water into street sewer systems to the north or west that drain into Rice Creek. Known incidences of temporary pumping occurred in 1984, 1986 and 2002. In 2003, the City retained a hydrology firm, URS, to propose a permanent pumping and maintenance plan for Karth Lake. The City submitted URS’ report to the DNR in support of DNR permit #2003-3078. That permit allowed construction of a permanent pumping facility and adopted URS’ proposed parameters for operating the pump (the DNR Pumping 1 Contributors to the Project include the Karth Lake Improvement District Board (KLIDB), City of Arden Hills (City), Minnesota Department of Natural Resources (DNR), Rice Creek Watershed District (RCWD) and Houstin Engineering (HE). HE is a hydrology consulting firm retained by RCWD to assist with the Project under a Minnesota Pollution Control Agency (MPCA) Stormwater, Wastewater, and Community Resiliency grant. 2 These impervious surfaces cause a nearly immediate lake level rise of 2.25 inches for every 1.0 inch of rain. During periods of frequent and quick rains, run-off from the rest of the watershed can cause the lake level to rise by as much as a 4:1 multiple of rainfall.